The magnetic properties of magnetic recording media are dependent on the crystallographic texture and microstructure of the magnetic recording layer, which, in turn, are influenced by the underlayers in the medium (Laughlin, et al., 1991). Longitudinal magnetic recording media for use in computer disc drives are typically formed on a rigid substrate and include an underlayer over which a magnetic recording layer is deposited. The underlayer strongly influences the crystallographic texture and microstructure of the magnetic recording layer (Fang, Lee, Laughlin, et al., 1991).
A typical underlayer in such media is composed of chromium which provides a crystalline template texture with lattice matching for epitaxial deposition of some conventional cobalt-based alloys used in forming the overlying magnetic layer. In this way, the desired c-axis orientation of hexagonal-close packed phase of cobalt alloys can be achieved, which induces in-plane magnetization, desirable for longitudinal recording.
One approach to improving lattice matching between the underlayer and the magnetic layer has been to deposit underlayers composed of a chromium alloy having closer lattice matching with the overlying magnetic layer. For example, V has been added to chromium to improve its lattice match with CoCrPt (Parker, et al., 1993).
Another approach has been to deposit of an underlayer formed of an element other than chromium. For example, an underlayer of Ge has been described for use with a CoCr magnetic alloy for perpendicular magnetic recording (Futamoto, et al., 1987).
Another approach to enhancing magnetic properties by improving the lattice matching between the underlayer and the magnetic layer is by controlling the sputter deposition conditions of the underlayer. For example, chromium underlayers deposited at low substrate temperature and high deposition pressure form thick, columnar structures with voided boundaries for reduced exchange coupling and reduced noise (Doerner, et al., 1993).
More recently, deposition of an interlayer between the magnetic layer and the underlayer has been suggested (Fang, Lee). Lee describes the use of an NiAl underlayer for inducing better in-plane c-axis texture in CoCrPt films. A Cr intermediate layer is deposited between the NiAl underlayer and the CoCrPt layer to modify the interface structure between the two layers without disrupting the existing epitaxial relation between the NiAl and CoCrPt layers.
Fang describes a medium having an intermediate layer of Co or CoCrTa (84/13/3) deposited between a chromium underlayer and a CoCrPt magnetic layer. The intermediate layer in Fang also serves as a magnetic recording layer, since cobalt alloys containing chromium in this range have an appreciable saturation magnetization (Doerner, et al., 1993).